RAR archive of 470 KB named only A400, with no brand, board number or content type in the name. The model designation alone is too generic to identify the device reliably, so extract the files and confirm what they cover before use. Archives like this usually carry schematics or service sheets. Once matched to the hardware, they help trace power rails, measure voltages at test points, find protection components and work out which part is behind a short or no-power fault.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @cyberlanelectonik. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.